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🌐 漫画计算机网络基础

🎯 学习目标：掌握计算机网络核心原理，为分布式系统和网络编程打下坚实基础

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📋 目录

1. OSI七层模型与TCP/IP
2. HTTP/HTTPS协议详解
3. TCP/UDP协议机制
4. DNS解析与CDN原理
5. 网络安全基础

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🎭 漫画引言

小明: “为什么我的API调用有时候快有时候慢？”

架构师老王: “这就要从网络通信说起了！网络就像邮政系统，数据包就是信件…”

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🏗️ OSI七层模型与TCP/IP

🎨 漫画场景：网络邮政系统

   发送方                          接收方┌──────────┐                    ┌──────────┐│应用层 📱 │ ←→ HTTP请求/响应 ←→ │应用层 🖥️ │├──────────┤                    ├──────────┤│传输层 📦 │ ←→ TCP/UDP分段 ←→  │传输层 📦 │├──────────┤                    ├──────────┤│网络层 🗺️ │ ←→ IP路由选择 ←→   │网络层 🗺️ │├──────────┤                    ├──────────┤│数据链路层│ ←→ 以太网帧  ←→    │数据链路层│├──────────┤                    ├──────────┤│物理层 ⚡ │ ←→ 电信号传输 ←→   │物理层 ⚡ │└──────────┘                    └──────────┘

📚 网络协议栈实现

/*** 网络协议栈模拟器*/
public class NetworkProtocolStack {// 应用层 - HTTP协议static class ApplicationLayer {public HttpRequest createHttpRequest(String method, String url, String body) {HttpRequest request = new HttpRequest();request.method = method;request.url = url;request.body = body;request.headers.put("Content-Type", "application/json");request.headers.put("User-Agent", "Java-Client/1.0");System.out.println("应用层：创建HTTP请求 " + method + " " + url);return request;}public HttpResponse parseHttpResponse(String responseData) {HttpResponse response = new HttpResponse();String[] lines = responseData.split("\n");// 解析状态行String statusLine = lines[0];response.statusCode = Integer.parseInt(statusLine.split(" ")[1]);System.out.println("应用层：解析HTTP响应，状态码：" + response.statusCode);return response;}}// 传输层 - TCP协议static class TransportLayer {public List<TcpSegment> segmentData(byte[] data, int sourcePort, int destPort) {List<TcpSegment> segments = new ArrayList<>();int mss = 1460; // 最大分段大小for (int i = 0; i < data.length; i += mss) {int segmentSize = Math.min(mss, data.length - i);byte[] segmentData = Arrays.copyOfRange(data, i, i + segmentSize);TcpSegment segment = new TcpSegment();segment.sourcePort = sourcePort;segment.destPort = destPort;segment.sequenceNumber = i;segment.data = segmentData;segment.checksum = calculateChecksum(segmentData);segments.add(segment);}System.out.println("传输层：数据分段，共" + segments.size() + "个TCP段");return segments;}private int calculateChecksum(byte[] data) {int checksum = 0;for (byte b : data) {checksum += b & 0xFF;}return checksum & 0xFFFF;}}// 网络层 - IP协议static class NetworkLayer {public IpPacket createIpPacket(TcpSegment segment, String sourceIp, String destIp) {IpPacket packet = new IpPacket();packet.version = 4; // IPv4packet.headerLength = 20;packet.totalLength = 20 + segment.data.length;packet.sourceIp = sourceIp;packet.destIp = destIp;packet.protocol = 6; // TCP协议号packet.payload = segment;System.out.println("网络层：创建IP数据包 " + sourceIp + " -> " + destIp);return packet;}public String routePacket(IpPacket packet) {// 简化的路由选择String[] destParts = packet.destIp.split("\\.");int network = Integer.parseInt(destParts[0]);if (network == 192) {System.out.println("网络层：本地网络，直接投递");return "local";} else {System.out.println("网络层：远程网络，通过路由器转发");return "router";}}}// 数据结构定义static class HttpRequest {String method;String url;String body;Map<String, String> headers = new HashMap<>();}static class HttpResponse {int statusCode;String body;Map<String, String> headers = new HashMap<>();}static class TcpSegment {int sourcePort;int destPort;long sequenceNumber;long acknowledgmentNumber;byte[] data;int checksum;}static class IpPacket {int version;int headerLength;int totalLength;String sourceIp;String destIp;int protocol;Object payload;}
}

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🌐 HTTP/HTTPS协议详解

📡 HTTP协议工作流程

/*** HTTP协议模拟器*/
public class HttpProtocolSimulator {// HTTP客户端static class HttpClient {private Socket socket;public HttpResponse sendRequest(String host, int port, HttpRequest request) {try {// 建立TCP连接socket = new Socket(host, port);System.out.println("建立TCP连接：" + host + ":" + port);// 发送HTTP请求PrintWriter out = new PrintWriter(socket.getOutputStream(), true);BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));// 构造HTTP请求报文StringBuilder requestBuilder = new StringBuilder();requestBuilder.append(request.method).append(" ").append(request.path).append(" HTTP/1.1\r\n");requestBuilder.append("Host: ").append(host).append("\r\n");requestBuilder.append("Connection: keep-alive\r\n");for (Map.Entry<String, String> header : request.headers.entrySet()) {requestBuilder.append(header.getKey()).append(": ").append(header.getValue()).append("\r\n");}requestBuilder.append("\r\n");if (request.body != null) {requestBuilder.append(request.body);}System.out.println("发送HTTP请求：\n" + requestBuilder.toString());out.print(requestBuilder.toString());out.flush();// 接收HTTP响应HttpResponse response = parseResponse(in);return response;} catch (IOException e) {System.err.println("HTTP请求失败：" + e.getMessage());return null;}}private HttpResponse parseResponse(Buffer